We want to always resolve TGS requests even if the user mistakenly sends a
request for a service ticket where the fqdn part contain upper case letters.

The actual implementation follows hints set by KDC. When AP_REQ is done, KDC
sets KRB5_FLAG_ALIAS_OK and we obey it when looking for principals on TGS requests.

https://fedorahosted.org/freeipa/ticket/1577

This was introduced when we started checking the return from
ipadb_get_context() to silence another coverity report.
That condition can never be true in this function but whatever ... let's
silence Coverity once again :)

We were using the wrong principal in the s4u2proxy case.

Fixes: https://fedorahosted.org/freeipa/ticket/2504

This was causing the failure count interval to not be applied so
the failure count was never reset to 0.

https://fedorahosted.org/freeipa/ticket/2540

Some of these are not real defects, because we are guaranteed to have valid
context in some functions, and checks are not necessary.
I added the checks anyway in order to silence Coverity on these issues.

One meleak on error condition was fixed in
daemons/ipa-kdb/ipa_kdb_pwdpolicy.c

Silence errors in ipa-client/ipa-getkeytab.c, the code looks wrong, but it is
actually fine as we count before hand so we never actually use the wrong value
that is computed on the last pass when p == 0

Fixes: https://fedorahosted.org/freeipa/ticket/2488